In color display devices employed for image display on computers or TVs, a plasma display device having a plasma display panel (hereinafter referred to as a PDP) has recently received considerable attention as a color display device with large sized screen but lightweight body due to its low-profile structure.
A PDP displays images in full color by performing an additive color process on red, green, and blue—known as the three primary colors. To realize the full color display, the PDP has phosphor layers that are respectively prepared for emitting red (R), green (G), and blue (B) of the three fundamental colors. A phosphor layer is formed of phosphor particles. The phosphor particles are excited by ultraviolet rays generated in a discharge cell in the PDP, so that visible lights of red, green, and blue are produced.
As the well-known chemical compounds for the phosphors above are: (Y,Gd) BO3:Eu3+, Y2O3:Eu3+ for emitting red; Zn2SiO4:Mn2+ for emitting green; and BaMgAl10O17:Eu2+, CaMgSi2O6:Eu for emitting blue. Each phosphor is manufactured through solid phase reaction; after mixed predetermined material, it is baked at high temperature beyond 1000° C. (for example, see Phosphor Handhook, pp 219 and 225, Ohmsha). Because the baking process sinters the phosphor particles, they should be crushed to a proper size before using: an average particle diameter of 2-5 μm for the red, and the green phosphors, 3-10 μm for the blue phosphor.
The prior-art phosphors above, however, have a problem—particularly in the blue phosphor formed of BaMgAl10O17:Eu, phosphor luminance decreases in the heating step of the phosphor layer-forming process or under panel operation. Employing the crystal structure of CaMgSi2O6:Eu system as the blue phosphor can slightly improve in the phosphor luminance in the heating step of the phosphor layer-forming process or in panel operation; however, the manufacturing method and the crystal structure by the conventional solid phase reaction has been facing the problem of low luminance—especially under panel operation, serious degradation in luminance occurs. The inconvenience comes from the fact that the blue emitting phosphor with the crystal structure of CaMgSi2O6:Eu is easy to undergo sintering, due to its low melting point, in the solid phase reaction. Therefore, there is no way, without crushing, to obtain a blue phosphor particle having the diameter less than 8 μm. In the solid phase reaction, the crystal of CaMgSi2O6:Eu as the phosphor should preferably be sintered at temperatures around 1400° C.; however, such a high temperature accelerates particle growth, allowing each particle to have a particle diameter of several ten μm. When the structure with a large particle diameter due to the sintering is crushed to obtain a particle diameter less than 3 μm, a structural defect developed in the crystal seriously impairs the luminance. The problem above has been an obstacle to realizing an improved panel having high luminance and minimizing luminance degradation under panel operation. The problem above also shortens the lifetime of the panel.
The present invention addresses the inconvenience above. It is therefore the object to obtain the blue emitting phosphor with high luminance. Also, it is another object to provide a panel that can minimize degradation in luminance.